class D(object):
    pass
class F(object):
    pass
class E(object):
    pass

class C(D, F):
    pass
class B(E, D):
    pass

class A(B, C):
    pass
print(A.__mro__)

'''
解决的问题：单调性问题，不能重写问题

拓扑排序思想
'''
